Searches for low-mass Higgs and dark bosons at BaBar Benjamin Oberhof, INFN & Università di Pisa, on behalf of the BaBar Collaboration QCD 2012, 2-6 July 2012, Montpellier, France
Outline The BaBar experiment & datasample Searches for GeV-scale dark matter candidates Searches for a light CP-odd Higgs 2
The BaBar Experiment PEP-II asymmetric B-factory at SLAC running (mainly) at the Υ(4S)=10.58 GeV with CM boost βγ = 0.55 Total Luminosity: ~530 fb-1 Peak Luminosity: 12x1033 cm-2 s-1 Data taking 1998 2008 Total data sample ~531 fb-1: - 470x106 Υ(4S) decays - 120x106 Υ(3S) decays - 100x106 Υ(2S) decays - 25x106 Υ(1S) from Υ(2,3S)->π+π-Υ(1S) decays 3
The Dark Sector Many evidences of dark matter from astrophysical experiments (PAMELA, DAMA, FERMI) New models introducing a dark force mediated by a new gauge boson with O(GeV) mass have been proposed (Phys. Rev. D 79 015014, 2009) The dark boson can mix kinetically with the SM photon with strength ε Photon Dark Boson Higgs mechanism generates boson mass adding one or more (depending on model) dark Higgs(es) to the theory WIMP-like particles can annihilate to dark bosons which in turn annihilate to SM fermion pairs This dark sector scenario can be tested at low-energy e+e- colliders 4
Search for Dark Higgs at BaBar Higgs-strahlung: Suppressed Small only by ε2 factor expected background Event Selection (2 ways): Full reconstruction: - A e+e, μ+μ-, π+π-, - 6 tracks with an invariant mass mtot>0.95 s Partial reconstruction: - 2 A decaying to leptons and 1 A to qq, A1 e+e, μ+μ-, A2 μ+μ, A3 X (X l+l or π+π-) - 4 or more tracks - Reconstructed four momentum p3=pee p1 p2 3 A' candidates must have same mass Signals: 6µ, 4µ2e, 2µ4e, 6e, 4µ2π, qq dominant for at high ma' 2µ2e2π, 4e2π, 2µ4π, 2e4π, 4µ+X, 2µ2e+X 5
Search for Dark Higgs: Results Search for dark Higgs with mh' > 2mA' 0.8 < mh'< 10 GeV, 0.25 < ma'< 3.0 GeV Complete (Y(4S), Y(3S), Y(2S)) data sample used 6 candidate signal events No event with 6 leptons Consistent with background only expectation from control samples ω and φ resonance regions masked σ (e+e- h'a', h' A'A') < 10-100 ab at 90% CL αdε2 < 10-9-10-6 at 90% CL Phys. Rev. Lett. 108, 211801 (2012) 6 3 entries plotted for every event
Search for Dark Higgs: Limits Phys. Rev. Lett. 108, 211801(2012) ma' Limits on DS-SM coupling as function of mh' and ma' αd=gd/4π dark sector coupling αdε2 < 10-9-10-6 at 90% CL αd=αsm assumed mh' 7
Light Higgs: Motivation Light CP-odd Higgs arise in several beyond SM scenarios: NMSSM: adds singlet Higgs field to MSSM - Solves hierarchy problem - Results in an additional CP-odd Higgs that mixes with the MSSM Higgs Light CP-odd Higgs can be directly produced in Y(nS) γa0, where A0 SM particles Models can evade LEP constraints still predicting large BF Also low mass Dark Matter candidates (χ) can be directly produced in the transition: - Y(nS) χχ - Y(nS) γχχ (J. Gunion et al., PRD 73, 015011 (2006)) 8
Light Higgs at BaBar BR(A0 gg) Search is done in the decay of the light and narrow Y(nS) resonances Dominant decay of the light CP-odd Higgs will depend on ma0 and tanβ Different final states studied by BaBar A0 µ+µ-, τ+τ-, hadronic, invisible BR(A0 ss) Phys. Rev.D 81, 075003 (2010) BR(A0 µµ) BR(A0 ττ) 9 BR(A0 cc)
Light Higgs at BaBar Event Tagging 2-body radiative decays of Y states, Y(2, 3S) γa0 (n=1,2,3): - Signature: monochromatic photon in the CM frame Y(2, 3S) ππy(1s), Y(1S) Invisible+γ or µ+µ-γ - Signature: exactly 2 tracks, with common vertex, identified as pions - Fit recoil mass M2REC= s+m2ππ-2e*ππ s Y(2, 3S) γa0, A0 µ+µprl 103, 081803 (2009) Y(2, 3S) γa0, A0 τ+τprl 103, 181801 (2009) Y(2, 3S) γa0, A0 hadrons PRL 107, 221803 (2011) Y(2, 3S) ππy(1s), Y(1S) γµ+µ- (NEW) Y(2, 3S) ππy(1s), Y(1S) Invisible + γ PRL 107, 021804 (2011) Y(2, 3S) ππy(1s), Y(1S) Invisible PRL 103, 251801 (2009) (search for dark matter candidates) 10
Υ(2S,3S) γa, A μ μ or A τ τ 0 0 PRL 103, 081803 (2009) A0 μ+μ- + - 0 + - J/Ψ, ψ(2s) excluded NO SIGNIFICANT SIGNAL B(Y(2S) γa0, A0 μ+μ- )<(0.26-8.3)x10-6 B(Y(3S) γa0, A0 μ+μ- )<(0.27-5.5)x10-6 at 90% CL PRL 103, 181801 (2009) A0 τ+τno SIGNIFICANT SIGNAL B(Y(2S,3S) γa0, A0 τ+τ- ) <(1.5-16)x10-5 at 90%CL χbj(2p) excluded 11
Limits for leptonic Υ(2,3S) decays PS exclusion regions in NMSSM for leptonic A0 decays tanβ=10, M1,2,3 =100, 200, 300 GeV assumed A0 τ+τ- 12 A0 μ+μ-
Υ(2S,3S) γa, A hadrons 0 Selection: Eγ>0.2 GeV and at least 2 tracks Full event energy reconstructed 0 PRL 107, 221803 (2011) CP-all Beam energy and momentum constraints FIT Continuum Data Considered both CP-odd (no K+Kor π+π-) and CP-all hypotheses CP-odd Fit and scan hadronic A0 mass from 0.29 to 7.1 GeV CP-all UL NO SIGNIFICANT SIGNAL Exp. UL B(Y(2,3S) γa, A had)<(0.1-8)x10 at 90% CL (with the assumption of same matrix element for n=2, 3) 0 0-5 13 Stat only CP-odd
Υ(1S) A, A Invisible+γ 0 0 Y(2,3S) π+π-y(1s), Y(1S) Invisible+γ - Eγ>150 MeV - 2D fit to ππ recoil mass & missing mass - Max significance: 2.0σ, at ma=7.58gev - 30% probability to observe this peak anywhere PRL 107, 021804 (2011) Recoil Mass NO SIGNIFICANT SIGNAL B(Y(1S) γα0,α0 Invisible)<(1.9-37)x10-6 B(Y(1S) γχχ)<(0.5-24)x10-5 at 90% CL 2.0σ, 7.58GeV B(Y(1S) γχχ) B(Y(1S) γα0 Α0 Invisible) 14 Missing Mass
NEW! BaBar preliminary Υ(1S) γa0, A0 μ+μ- We search for Y(2, 3S) π+πy(1s) where Y(1S) γa0 and A0 µ+µ- Di-pion tag Eγ>200 MeV Fit on the reduced mass Signal Y(2S) Background Y(3S) 14 15
Υ(1S) γa, A μ μ NEW! 0 0 + - BaBar preliminary Compatible with bkg only hypothesis NO SIGNIFICANT SIGNAL Y(2S) UL at 90% CL Y(2S) data: B(Y(1S) γa0, A0 μ+μ-) <(0.37-9.05)x10-6 Y(3S) Y(3S) data:b(y(1s) γa0, A0 μ+μ-) <(1.16-24.24)x10-6 Combined: B((Y(1S) γa0, A0 μ+μ-) <(0.22-10.38)x10-6 Combined 16
Summary Searches for: CP-odd light Higgs in the Y(1s), Y(2S) and Y(3S) radiative decays Dark matter candidates No significant signal of light Higgs or light Dark Matter observed Upper limits have been set with improvements over previous measurements Excluded new portions of parameter space for some NP models Additional analyses are ongoing at BaBar, new results expected in near future 17
Backups 18
BaBar Datasample Total data sample ~531 fb-1: - 470x106 Υ(4S) decays - 120x106 Υ(3S) decays - 100x106 Υ(2S) decays - 25x106 Υ(1S) from Υ(2,3S)->π+π-Υ(1S) decays 19
Astrophysical evidence for DM 20
Search for Dark Higgs: Results Expected Background Limits 21
Υ(2S,3S) γa0, A0 μ μ or A0 τ τ + - A0 μ+μ- + - PRL 103, 081803 (2009) - 2 tracks, forming vertex & muon PID - Eγ>200 MeV - Fit and scan of the μ+μ- invariant mass A0 τ+τprl 103, 181801 (2009) - Considers both τ eνν and τ μνν - Eγ>100 MeV and 2 tracks identified as leptons - Missing energy precludes kinematic fit; A0 mass obtained from Eγ and known CM energy - Fit and scan in Eγ spectrum between4.03 < ma0 < 10.10 GeV/c2 22
Υ(1S) A0, A0 invisible+γ 23
DM Search in Y(1s) -> Invisible Analysis Strategy: - Tag Y(1s) from pions emitted in Y(3s)->Y(1s) π+π-υ(1s) - We want 2 charged tracks and nothing else - Signal: Υ(3S) π+π-υ(1s), Y(1s)->Invisible Backgrounds: - Non-peaking background from random π+π combinations - Peaking background (indistinguishable from signal), Υ(3S) π+π-υ(1s), Υ(1S) X (X undetected) Signal Extraction: - Recoil mass Mrec=(s+M2ππ - 2sE*ππ)1/2, should peak at Υ(1S) - Subtract peaking background estimated from MC. -MC-Data matching is crucial: use Υ(1S,2S) l+l- with one or two reconstructed leptons to correct simulation. 24
DM Search in Y(1s) -> Invisible 25
Direct Search for Dark Bosons ArXiv:0908.2821, BABAR preliminary We search for: ℓ=e, µ e+e- W'W' (ℓ+ℓ-)(ℓ+ℓ-) 4 leptons of zero total charge, carrying full beam energy and momentum 2 di-lepton resonances with same mass Cut-and-count analysis in terms of (m1+m2) and (m1-m2) Full datasample used NO SIGNIFICANT SIGNAL σ (e+e- W'W' ℓ+ℓ-ℓ+ℓ-) < 25-60 ab at 90% CL gdε2 < 10-9-10-7 at 90% CL 26